1. Field of the Invention
This invention relates to a fuel metering control system for an internal combustion engine.
2. Description of the Related Art
Japanese Laid-Open Patent Application Hei 3(1991)-185,244 teaches installing at the exhaust system of the engine a first oxygen sensor (that detects the exhaust air/fuel ratio in a wide range) upstream of a catalytic converter and a second oxygen sensor (O.sub.2 sensor) downstream of the catalytic converter. In the proposed control, a desired air/fuel ratio is established such that the catalytic purification efficiency becomes maximum within an air/fuel ratio window (so-called "catalyst window") determined on the basis of outputs of the second oxygen sensor (O.sub.2 sensor). Fuel metering is controlled in response to an error between the established air/fuel ratio and outputs of the first oxygen sensor (wide-range oxygen sensor). This proposed control uses an optimum regulator in fuel metering control.
The prior art system is configured such that the desired air/fuel ratio change is followed by feedback control. Since, however, the system is unable to follow the change in dynamic characteristics due to aging or manufacture variance of the engine, the prior art has the drawback that it is not possible to achieve optimal control performance. This is because the air/fuel ratio behavior is not adaptively ensured in the prior art system. In addition, the fuel adhesion correction is not conducted in the prior art system, therefore it can not sufficiently cope with the fluctuation of air/fuel ratio due to the fuel transport delay.